Control device for an asynchronous electric machine, electric propulsion system comprising said device, and method for controlling an asynchronous electric machine

Abstract

A control device for an asynchronous electric machine comprising a first computing unit configured for defining a first signal, indicating a desired slip frequency of the electric machine, as a function of a second signal correlated to a reference input velocity supplied through a user interface, and of a third signal correlated to a detected rotor angular velocity, the control device preferably comprising a user interface for supplying the second signal and a velocity-detection module coupled to the electric machine for supplying the third signal.

1 . A control device for an asynchronous electric machine ( 2 ), comprising a first computing unit ( 14 ) configured for defining a first signal (S 3 ), indicating a desired slip frequency (fsd) of the electric machine ( 2 ), as a function of a second signal (S 6 ) correlated to a reference input velocity (ωi) supplied through a user interface ( 6 ), and of a third signal (S 4 ) correlated to a detected rotor angular velocity (ωr); the control device ( 5 ) preferably comprising the user interface ( 6 ) for supplying the second signal (S 6 ), and a velocity-detection module ( 9 ) coupled to the electric machine ( 2 ) for supplying the third signal (S 4 ). 
     
     
         2 . The control device according to  claim 1 , wherein the first computing unit ( 14 ) is configured for defining the first signal (S 3 ) on the basis of a fourth signal (S 8 ) correlated to a reference voltage (Vr); the control device ( 5 ) preferably comprising a voltage-metering module ( 8 ) designed to supply the fourth signal (S 8 ). 
     
     
         3 . The control device according to  claim 1 , wherein the first computing unit ( 14 ) is designed to define the first signal (S 3 ) as a function of a fifth signal (S 7 ) supplied by the user interface ( 6 ) and correlated to a command for braking the electric machine ( 2 ). 
     
     
         4 . The control device according to  claim 1 , wherein the first computing unit ( 14 ) comprises a first computing module ( 21 ) configured for defining a sixth signal (S 9 ) indicating a velocity error (ERR) from the comparison between the second signal (S 6 ) with the third signal (S 4 ); and wherein the first computing unit ( 14 ) comprises a second computing module ( 22 ) configured for defining a seventh signal (S 10 ) obtained by amplifying the sixth signal (S 9 ) with a gain variable as a function of the third signal (S 4 ). 
     
     
         5 . The control device according to  claim 4 , wherein the first computing unit ( 14 ) comprises a third computing module ( 23 ) for calculating an acceleration on the basis of the third signal (S 4 ) and for supplying an eighth signal (S 11 ) obtained by processing the seventh signal (S 10 ) on the basis of the acceleration calculated and on the basis of a ninth signal (S 12 ) supplied by the user interface ( 6 ) and indicating a command for reduction of consumption. 
     
     
         6 . The control device according to  claim 5 , wherein the first computing unit ( 14 ) comprises a fourth computing module ( 24 ) configured for defining a tenth signal (S 13 ) on the basis of the eighth signal (S 11 ), of the third signal (S 4 ), of the second signal (S 6 ), and of a fifth signal (S 7 ). 
     
     
         7 . The control device according to  claim 6 , wherein the first computing unit ( 14 ) comprises a fifth computing module ( 26 ) for defining the first signal (S 3 ) obtained by processing the tenth signal (S 13 ) on the basis of the fourth signal (S 8 ) and on the basis of the third signal (S 4 ) so as to limit the desired slip frequency (fsd) of the electric machine ( 2 ) to a maximum value as a function of the third signal (S 4 ) and on the basis of a fourth signal (S 8 ) correlated to a reference voltage (Vr). 
     
     
         8 . The control device according to  claim 1 , comprising a second computing unit ( 10 ) configured for defining an eleventh signal (S 1 ), correlated to an operating voltage (V) to be applied to the electric machine ( 2 ), as a function of a twelfth signal (S 2 ) indicating a desired stator frequency (f 1 d) of the operating voltage (V), and as a function of the first signal (S 3 ) indicating the desired slip frequency (fsd) of the electric machine ( 2 ). 
     
     
         9 . The control device according to  claim 8 , wherein the second computing unit ( 10 ) comprises at least one port ( 11 ,  12 ) for receiving at input the twelfth signal (S 2 ) and the first signal (S 3 ). 
     
     
         10 . The control device according to  claim 8 , comprising a fourth computing module ( 13 ) for defining the twelfth signal (S 2 ) on the basis of the first signal (S 3 ) and of the third signal (S 4 ) correlated to a detected rotor frequency, preferably by adding the desired slip frequency (fsd) indicated by the first signal (S 3 ) to the detected rotor frequency. 
     
     
         11 . The control device according to  claims 8 , wherein the second computing unit ( 10 ) is configured for supplying a respective first value of the operating voltage (V) and a respective second value of the operating voltage (V) for each admissible value of a first desired quantity chosen between the desired slip frequency (fsd) and the desired stator frequency (f 1 d) of the electric machine ( 2 ). 
     
     
         12 . The control device according to  claim 11 , wherein the second computing unit ( 10 ) is configured for defining a set of voltage values as a function of a value of the first desired quantity and of the first value and of the second value of the operating voltage (V) associated to the value of the first desired quantity, and for defining a value of the eleventh signal (S 1 ), comprised in a set of voltage values, as a function of a value of a second desired quantity chosen between the desired stator frequency (f 1 d) and the desired slip frequency (fsd) and distinct from the first desired quantity. 
     
     
         13 . The control device according to  claim 12 , wherein the second computing unit ( 10 ) is configured for defining the value of the eleventh signal (S 1 ) on the basis of: a zero value of the desired slip frequency (fsd), if the first signal (S 3 ) indicates a negative value of the desired slip frequency (fsd); and 
       a value of the desired slip frequency (fsd) deriving from the value of desired slip frequency (fsd) defined by the first signal (S 3 ) and modified on the basis of a thirteenth signal (S 5 ) supplied by the user interface ( 6 ), if the first signal (S 3 ) indicates a positive value of the desired slip frequency (fsd). 
     
     
         14 . An electric propulsion system comprising: an asynchronous electric machine ( 2 ); a source of electrical energy ( 3 ) for supplying the asynchronous electric machine ( 2 ); and a control device ( 5 ) according to  claim 1 . 
     
     
         15 . The electric propulsion system according to  claim 14 , comprising power switches ( 4 ) arranged between the source of electrical energy ( 3 ) and the electric machine ( 2 ) for supplying an operating voltage (V) to the electric machine ( 2 ), and a control unit ( 7 ) for the power switches ( 4 ) configured for controlling the power switches ( 4 ) so as to supply the operating voltage (V) on the basis of the first signal (S 3 ) defined by the first computing unit ( 14 ); the control unit ( 7 ) preferably receiving at input a fourth signal (S 8 ) indicating a reference voltage (Vr) of the source of electrical energy ( 3 ) and acting on the power switches ( 4 ) on the basis of the value of the reference voltage (Vr) of the source of electrical energy ( 3 ). 
     
     
         16 . A method for controlling an asynchronous electric machine ( 2 ), comprising the step of defining a first signal (S 3 ), indicating a desired slip frequency (fsd) of the electric machine ( 2 ), as a function of a second signal (S 6 ) correlated to a reference input velocity (ωi) supplied through a user interface ( 6 ), and of a third signal (S 4 ) correlated to a detected rotor angular velocity (ωr). 
     
     
         17 . The method according to  claim 16 , comprising the steps of: detecting a reference voltage (Vr) of the source of electrical energy ( 3 ) coupled to the electric machine ( 2 ); and defining the first signal (S 3 ) on the basis of the reference voltage (Vr). 
     
     
         18 . The method according to  claim 16 , the first signal (S 3 ) is defined as a function of a fifth signal (S 7 ) supplied by the user interface ( 6 ) and correlated to a command for braking the electric machine ( 2 ). 
     
     
         19 . The method according to  claim 16 , comprising the steps of: defining a velocity error (ERR) from the comparison between the detected rotor angular velocity (ωr) and the reference input velocity (ωi); and amplifying the velocity error (ERR) with a gain variable as a function of the detected rotor angular velocity (ωr). 
     
     
         20 . The method according to  claim 19 , comprising the steps of: calculating an acceleration on the basis of the detected rotor angular velocity (ωr); and limiting the velocity error (ERR) amplified on the basis of the acceleration calculated and on the basis of a ninth signal (S 12 ), which is supplied by the user interface ( 6 ) and indicates a command for reduction of consumption. 
     
     
         21 . The method according to  claim 20 , comprising the step of defining a tenth signal (S 13 ) on the basis of the limited velocity error (ERR), of the reference input velocity (ωr), and of a command for braking the electric machine ( 2 ). 
     
     
         22 . The method according to  claim 21 , wherein the step of defining the first signal (S 3 ) comprises processing the tenth signal (S 13 ) on the basis of the reference voltage (Vr), and on the basis of the detected rotor angular velocity (ωr) so as to limit the desired slip frequency (fsd) of the electric machine ( 2 ) to a maximum value, which is a function of the detected rotor angular velocity (ωr) and of the reference voltage (Vr).